Did you ever look at your husband or wife and feel that person is an impostor? Janet, a 24-year-old graduate student, came home from a stressful day at school and found a man she thought was a stranger in her bed.

"Who are you? How did you get into my apartment?" she asked.

She was in no mood to fool around with a strange man who had somehow gained entrance to her apartment and was lounging on her bed in her husband's blue silk pajamas.

"Very funny. And who are you?"

The man countered. He looked similar to Dave, her husband. In fact, he had short brown hair, dark blue eyes and the same kind of round cheeks as Dave. However, Janet knew in her gut that it wasn't Dave. Maybe distant relatives or casual friends might believe the man was Dave, but Janet and Dave had been together practically every day for the last three years, and Janet could swear it wasn't her husband.

As a psychiatrist I treat many bizarre conditions, but this case was one of the strangest. The movie "Invasion of the Body Snatchers," in which people correctly accuse their loved ones of being impostors, illustrates Capgras' syndrome. In the movie, the townspeople's loved ones were actually replaced by extraterrestrials who want to destroy humanity. In Capgras' syndrome, people falsely believe their loved ones are replaced by duplicates.

"You better explain yourself quickly because I'm calling the police," she said, reaching for her cell.

Janet looked around frantically for her husband, whom she thought might arrive any second and be angry with her for having a strange man in the apartment.

"The police! Are you flipping out? Come over here and cut out this nonsense. There's a great movie we can watch."

He patted the bed for her to sit down in the same way that Dave would have.

Then it occurred to her, as she stared at him, that her husband had somehow been replaced by this individual, who was a close duplicate of Dave. How this had happened, she didn't know; she only knew it was true.

The next day in my office, she told me what had happened.

"Did you take your medicine?" I asked, worried that she was de-compensating.

Janet revealed that she hadn't taken her Seroquel, an antipsychotic, for the last few days, because the side effects of weight gain and sleepiness were disturbing her.

"You must take your medicine every day," I said as patiently as I could.

She said she believed me, but she couldn't stand to be on medicine. Janet had schizophrenia, which meant that she could lose contact with reality and have hallucinations and delusions, which are fixed, false beliefs. Delusions, like Capgras, are part of the condition.

"I don't want to be fat," she explained. "Also I have exams next week, and it's hard to study and stay awake on that medicine."

I tried to make her promise that she would restart her medicine. Suddenly she sat back and stared at me.

"What happened?" I asked.

"My parents looked kind of funny the other day, too. I think they've been replaced by impostors, just like Dave," she blurted out and then ran out of my office before her session was done.

She wouldn't answer my calls, but Dave called in a few days and reported that Janet was going "crazy" again, believing that he and also her parents had been replaced by duplicates. Janet had gone "crazy" a few times before when she stopped her medicine.

Unfortunately, I had to hospitalize her and restart her medicine on the ward.

My patient suffered from a variation of Capgras' syndrome, in which patients believe their loved ones are replaced by inexact duplicates. The original delusional disorder was described in 1923 by the French psychiatrists Capgras and Reboul-Lachaux. They treated a 53-year-old woman who believed that her husband, children, neighbors and even herself had been replaced by exact "doubles" as a part of a plot to steal her property. In "Invasion of the Body Snatchers," the Pod people, perfect physical duplicates of the townspeople, kill and dispose of their human victims. My patient did not think that Dave or her family meant her any harm, but she still had Capgras' syndrome.

In Capgras there is an uncoupling of perception and recognition that leads many doctors to believe there may be a neuro-physiological, organic cause, which thus far remains unknown. Psychoanalysts have seen Capgras as an unusual form of displacement where a patient rejects a loved one whenever negative features show up. Like my patient, the person with Capgras cannot allow herself to become conscious of the rejection because of guilt and ambivalence. The bad feelings are displaced to a double, who is an impostor and may safely be rejected.

This splitting mechanism results in Capgras' doubles. Anna Freud thought patients were defending against loss and distress about changes in close relationships by adapting a doubles delusion.

Janet no longer believed that Dave and her parents were doubles after she restarted her medicine. She was discharged from the hospital and went on to complete her studies. She always felt uncomfortable, though, and thought that it was possible that a stranger could someday replace her husband.

Carol W. Berman, MD is a writer, psychiatrist and artist who lives and works in New York City. When she's not listening to patients, she's writing or painting. As an undergraduate she attended the University of California at Berkeley; she went to medical school at NYU Medical Center. Presently she is an Assistant Clinical Professor at NYU. She has practiced psychiatry for 25 years and is a member of the APA, ASJA and NWU. Her book, 100 Questions and Answers About Panic Disorder, Second Edition has helped thousands of patients deal with mental disorders.